The purpose of this study is to determine whether vaccination with NicVAX will result in a higher continuous abstinence rate than vaccination with placebo in smokers who want to quit smoking. In addition, two different formulations and dosing schedules will be studied, to select the dose and dosing schedule which generates the highest level of anti-nicotine antibodies. The primary study period is 12 months, which was extended by amendment to include up to 2 years of observations.